Devices and methods for fuel detection have been used increasingly often. U.S. Pat. No. 5,958,780 discloses a method of identifying liquids, such as gasoline or other oil byproducts, by introducing miscible markers into these liquids, and subsequently identifying the same by analyzing the concentration of the marker through absorption spectrometry. The presence and concentration of these markers would indicate the addition or absence of solvents. Patent PI 0406097-0 A proposes measuring the anhydrous ethyl alcohol fuel (AEAF) concentration by means of the electrical conductivity or resistivity of the fuel itself. Patent PI 8405986 proposes measuring the fuel concentration by measuring the dielectric constant of the mixture. Apparatuses and processes based on optical fiber sensors for liquid detection have been frequently conceived. Patent PI 3058301 A discloses an optical system for detecting and identifying liquids through the principle of reflectivity, while patent PI-5040213 A uses the same method for detecting and/or identifying leakages in fuel and beverage tanks. Patent PI 8702079 A proposes a method for detecting the ratio of the gasoline-ethanol mixture by measuring the critical angle of an incident beam of an optical system. Patent PI 8803374 A proposes a thermally-compensated method for detecting the gasoline-ethanol mixture ratio through an optical system which determines the refractive index of the fuel mixture. Patent PI 9200613 A proposes a thermally-compensated system for precisely detecting the mixture between two types of liquid fuels by measuring the refractive index of the fuel mixture using an optical prism.
However, existing sensors for detection or identification of liquids lack some important features and functionalities in terms of liquid fuels. For example, U.S. Pat. No. 5,958,780 determines the addition of special markers to the fuel and other components, such as to make its subsequent identification or concentration measurement possible by means of analysis in specialized laboratories and equipments. In the case of procedures mentioned in patents PI 0406097-0 A and PI 8405986 A, the latter employ the method of introducing electrical currents through fuels in order to determine the electrical conductivity or resistivity property, which may cause serious explosion hazards.
With regard to the identification of liquid fuel mixtures, such as adulterated fuels, or ethanol-gasoline flex-fuel automotive fuel mixture systems, or even the diesel-biodiesel mixture, there is a need for using highly-sensitive systems and sensor optical fibers. For example, systems disclosed in patents PI 305830-1 A and PI 504021-3 A, which were devised for detection and identification of leakages in fuel and beverage storage tanks, lack a higher sensitivity, due to limitations of the sensor fiber itself. Patent PI 8702079 A does not present a simple system for use in motor vehicles, and also assumes its use only in determining the ethanol-gasoline mixture ratio, without embracing mixtures between other types of fuel. The system proposed in patent PI 8803374 A requires three amplifiers to compensate for temperature variations. Lastly, patent PI-9200613 A uses an optical prism for determining the refractive index, as well as a bulky and complicated apparatus for supporting and coupling the same in motor vehicles.